U.S. patent application number 11/995325 was filed with the patent office on 2009-01-01 for pigment dispersions with polymeric dispersants having pending chromophore groups.
This patent application is currently assigned to AGFA GRAPHICS NV. Invention is credited to Geert Deroover, Lambertus Groenendaal, Wojciech Jaunky, Johan Loccufier.
Application Number | 20090005474 11/995325 |
Document ID | / |
Family ID | 35720781 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090005474 |
Kind Code |
A1 |
Jaunky; Wojciech ; et
al. |
January 1, 2009 |
Pigment Dispersions With Polymeric Dispersants Having Pending
Chromophore Groups
Abstract
A pigment dispersion includes a color pigment represented by
formula (I): ##STR00001## wherein R1 to R10 are independently
selected from the group consisting of hydrogen, a halogen atom, a
methyl group, an ethyl group, a methoxy group, an ethoxy group,
--CF3, --COOH, --COOCH.sub.3, --SO.sub.2NH--C.sub.6H.sub.5,
--CONH--C.sub.6H.sub.5, --CONH--C.sub.6H.sub.5--CONH.sub.2, and
--CONH.sub.2; and a polymeric dispersant, having via a linking
group covalently linked to its polymeric backbone, at least one
pending chromophore group which has a molecular weight smaller than
95% of the molecular weight of said color pigment. The pigment
dispersion can be advantageously used in inkjet inks.
Inventors: |
Jaunky; Wojciech; (Wesel,
DE) ; Deroover; Geert; (Lier, BE) ; Loccufier;
Johan; (Zwijnaarde, BE) ; Groenendaal; Lambertus;
(Sinaai, BE) |
Correspondence
Address: |
AGFA;c/o KEATING & BENNETT, LLP
1800 Alexander Bell Drive, SUITE 200
Reston
VA
20191
US
|
Assignee: |
AGFA GRAPHICS NV
Mortsel
BE
|
Family ID: |
35720781 |
Appl. No.: |
11/995325 |
Filed: |
June 23, 2006 |
PCT Filed: |
June 23, 2006 |
PCT NO: |
PCT/EP2006/063490 |
371 Date: |
January 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60713012 |
Aug 31, 2005 |
|
|
|
Current U.S.
Class: |
524/89 ; 524/171;
524/192 |
Current CPC
Class: |
C09B 67/009 20130101;
C09B 67/0063 20130101; C09B 69/10 20130101; C09B 69/106 20130101;
C09D 11/101 20130101; C09D 11/326 20130101; C09B 67/0046
20130101 |
Class at
Publication: |
524/89 ; 524/171;
524/192 |
International
Class: |
C08K 5/22 20060101
C08K005/22; C08K 5/41 20060101 C08K005/41; C08K 5/3417 20060101
C08K005/3417; C08K 5/3465 20060101 C08K005/3465 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 14, 2005 |
EP |
05106456.6 |
Claims
1-14. (canceled)
15: A pigment dispersion comprising a color pigment represented by
formula (I): ##STR00048## and a polymeric dispersant having, via a
linking group covalently linked to its polymeric backbone, at least
one pending chromophore group which has a molecular weight smaller
than 95% of the molecular weight of the color pigment; wherein R1
to R10 are independently selected from the group consisting of
hydrogen, a halogen atom, a methyl group, an ethyl group, a methoxy
group, an ethoxy group, --CF.sub.3, --COOH, --COOCH.sub.3,
--SO.sub.2NH--C.sub.6H.sub.5, --CONH--C.sub.6H.sub.5,
--CONH--C.sub.6H.sub.5--CONH.sub.2, and --CONH.sub.2.
16: The pigment dispersion according to claim 15, wherein the
pending chromophore group is represented by formula (II):
##STR00049## wherein one of L1, L2, or L3 is the linking group and
is selected from the group consisting of an aliphatic group, a
substituted aliphatic group, an unsaturated aliphatic group, and a
substituted unsaturated aliphatic group; L1, L2, and/or L3, if not
representing the linking group, are independently selected from the
group consisting of hydrogen, an alkyl group, an alkenyl group, an
alkoxy group, a carboxylic acid group, an ester group, an acyl
group, a nitro group, and a halogen; AR1 and AR2 represent an
aromatic group; and n represents the integer 0 or 1.
17: The pigment dispersion according to claim 15, wherein the
pending chromophore group is represented by Formula (III):
##STR00050## wherein one of R1 to R11 is the linking group forming
a covalent bond with the polymeric backbone; R1 to R11, if not
representing the linking group, are independently selected from the
group consisting of hydrogen, an alkyl group, an alkenyl group, an
alkoxy group, an alcohol group, a carboxylic acid group, an ester
group, an acyl group, a nitro group and a halogen; or R7 and R8 may
together form a heterocyclic ring.
18: The pigment dispersion according to claim 17, wherein the
heterocyclic ring formed by R7 and R8 is imidazolone or
2,3-dihydroxypyrazine.
19: The pigment dispersion according to claim 15, wherein the
linking group contains at least one atom selected from the group
consisting of an oxygen atom, a nitrogen atom, and a sulphur
atom.
20: The pigment dispersion according to claim 19, wherein the
linking group in unreacted form is represented by
--O--CH.sub.2--CH.sub.2--OH.
21: The pigment dispersion according to claim 20, wherein the
pending chromophore group represented by formula (III) having an
unreacted linking group is selected from the group consisting of:
##STR00051## ##STR00052## ##STR00053## ##STR00054##
22: The pigment dispersion according to claim 15, wherein the color
pigment is selected from the group consisting of C. I. Pigment
Yellow 155 and C. I. Pigment Yellow 198.
23: The pigment dispersion according to claim 15, wherein the
polymeric backbone of the polymeric dispersant is a
homopolymer.
24: The pigment dispersion according to claim 15, wherein the
pending chromophore group is present in the range of 1 to 30
percent based on the number of monomeric units of the polymeric
dispersant.
25: The pigment dispersion according to claim 15, wherein the
polymeric dispersant has a number average molecular weight Mn
between 500 and 30,000 and a polymeric dispersity PD smaller than
2.
26: The pigment dispersion according to claim 15, wherein the
pigment dispersion is an inkjet ink.
27: The pigment dispersion according to claim 15, wherein the
inkjet ink is a curable inkjet ink.
28: A method for preparing the inkjet ink according to claim 15,
comprising the step of preparing the polymeric dispersant by
copolymerizing a monomer already containing the pending chromophore
group.
Description
TECHNICAL FIELD
[0001] The present invention relates to stable pigment dispersions
and pigmented inkjet inks comprising colour pigments that are
stabilized by polymeric dispersants having pending chromophore
groups which exhibit a structural similarity with the colour
pigment.
BACKGROUND ART
[0002] Pigment dispersions are made using a dispersant. A
dispersant is a substance for promoting the formation and
stabilization of a dispersion of pigment particles in a dispersion
medium. Dispersants are generally surface-active materials having
an anionic, cationic or non-ionic structure. The presence of a
dispersant substantially reduces the dispersing energy required.
Dispersed pigment particles may have a tendency to re-agglomerate
after the dispersing operation, due to mutual attraction forces.
The use of dispersants also counteracts this re-agglomeration
tendency of the pigment particles.
[0003] The dispersant has to meet particularly high requirements
when used for inkjet inks. Inadequate dispersing manifests itself
as increased viscosity in liquid systems, loss of brilliance and/or
hue shifts. Moreover, particularly good dispersion of the pigment
particles is required to ensure unimpeded passage of the pigment
particles through the nozzles of the print head, which are usually
only a few micrometers in diameter. In addition, pigment particle
agglomeration and the associated blockage of the printer nozzles
has to be avoided in the standby periods of the printer.
[0004] Polymeric dispersants contain in one part of the molecule
so-called anchor groups, which adsorb onto the pigments to be
dispersed. In a spatially separate part of the molecule, polymeric
dispersants have polymer chains sticking out and whereby pigment
particles are made compatible with the dispersion medium, i.e.
stabilized.
[0005] The properties of polymeric dispersants depend on both the
nature of the monomers and their distribution in the polymer.
Polymeric dispersants obtained by randomly polymerizing monomers
(e.g. monomers A and B polymerized into ABBAABAB) or by
polymerizing alternating monomers (e.g. monomers A and B
polymerized into ABABABAB) generally result in a poor dispersion
stability. Improvements in dispersion stability were obtained using
graft copolymer and block copolymer-dispersants.
[0006] Graft copolymer dispersants consist of a polymeric backbone
with side chains attached to the backbone.
[0007] CA 2157361 (DU PONT) discloses pigment dispersions made by
using a graft copolymer dispersant with a hydrophobic polymeric
backbone and hydrophilic side chains.
[0008] Block copolymer dispersants containing hydrophobic and
hydrophilic blocks have been disclosed in numerous inkjet ink
patents.
[0009] U.S. Pat. No. 5,859,113 (DU PONT) discloses an AB block
copolymer dispersant with a polymeric A segment of polymerized
glycidyl (meth)acrylate monomers reacted with an aromatic or
aliphatic carboxylic acid, and a polymeric B segment of polymerized
alkyl (meth)acrylate monomers having 1-12 carbon atoms in the alkyl
group, hydroxy alkyl(meth)acrylate monomers.
[0010] In the design of polymeric dispersants for aqueous inkjet
inks, the above mentioned anchor groups, which adsorb onto the
pigments to be dispersed, are generally hydrophobic groups
exhibiting an affinity for the pigment surface.
[0011] EP 0763580 A (TOYO INK) discloses an aqueous type pigment
dispersing agent having a portion which has a high affinity with a
pigment and which has at least one type selected from the group
consisting of an organic dye, anthraquinone and acridone only at a
terminal end or at both terminal ends of at least one aqueous
polymer selected from the group consisting of an aqueous linear
urethane polymer and an aqueous linear acrylic polymer. EP 0763378
A (TOYO INK) discloses similar pigment dispersing agents for
non-aqueous pigment dispersions.
[0012] U.S. Pat. No. 5,420,187 (TOYO INK) discloses a
pigment-dispersing agent obtained by polymerizing an
addition-polymerizable monomer having an acidic functional group
and other addition-polymerizable monomer in the presence of a
polymerization initiator, the polymerization initiator being a
diazotization product prepared by diazotizing at least one compound
selected from the group consisting of an anthraquinone derivative
having an aromatic amino group, an acridone derivative having an
aromatic amino group and an organic dyestuff having an aromatic
amino group. In this pigment-dispersing agent, the colorant is
located in the polymeric backbone itself.
[0013] US 2003044707 (TOYO INK) discloses a dispersing agent for a
pigment, comprising a specific compound having a structure wherein
a phthalocyanine type molecular skeleton which is adsorptive on the
pigment and an oligomer unit or polymer unit which prevents
re-agglomeration of the pigment to bring out the effect of
dispersion are covalently bonded, and having affinity for a medium
or a solvent.
[0014] Current practice is that the exact or almost the exact
chemical structure of the colour pigment is incorporated as the
anchor group in the polymeric dispersing agent to assure maximum
affinity with the colour pigment. As a consequence, each pigment
has its own tailor made polymeric dispersant. In practice, this
requires the holding of an inventory of different polymeric
dispersants for producing a complete range of colour inkjet ink
sets. The cyan ink with copper phthalocyanine as pigment is a rare
exception in that all desired properties are combined in the same
pigment. But yellow pigments have to be selected based on the
properties that are the most important in their application of
inkjet ink. For example, some yellow pigments are selected for
their light stability, while others are selected to obtain images
having high colour strength. The holding of such an inventory of
different types of polymeric dispersants incurs financial penalties
due to additional storage and logistical requirements as well as
increasing the possibility of using the "wrong" polymeric
dispersant for the production of a particular inkjet ink. Another
disadvantage is that the low solubility of the pigment generally
complicates the synthesis of such polymeric dispersants.
[0015] For consistent image quality, the inkjet ink requires a
dispersion stability capable of dealing with high temperatures
(above 60.degree. C.) during transport of the ink to a customer and
changes in the dispersion medium of the inkjet ink during use, for
example, evaporation of solvent and increasing concentrations of
humectants, penetrants and other additives.
[0016] Therefore, it is highly desirable to be able to manufacture
a range of stable pigmented inkjet inks using a single polymeric
dispersant obtained by simple synthesis.
OBJECTS OF THE INVENTION
[0017] It is an object of the present invention to provide inkjet
inks using a polymeric dispersant obtained by uncomplicated
synthesis and suitable for different colour pigments.
[0018] It is a further object of the present invention to provide
inkjet inks with high dispersion stability.
[0019] It is a further object of the present invention to provide
inkjet inks producing images of high image quality with a high
optical density.
[0020] Further objects of the invention will become apparent from
the description hereinafter.
SUMMARY OF THE INVENTION
[0021] It has been surprisingly found that inkjet inks with high
optical density and high stability were obtained using a coloured
polymeric dispersant wherein a pending chromophore group exhibits a
structural similarity with the colour pigment, but is smaller in
size than the colour pigment.
[0022] Objects of the present invention have been realized with a
pigment dispersion comprising a colour pigment represented by
formula (I)
##STR00002##
[0023] wherein,
[0024] R1 to R10 are independently selected from the group
consisting of hydrogen, a halogen atom, a methyl group, an ethyl
group, a methoxy group, an ethoxy group, --CF.sub.3, --COOH,
--COOCH.sub.3; --SO.sub.2NH--C.sub.6H.sub.5,
--CONH--C.sub.6H.sub.5, --CONH--C.sub.6H.sub.5--CONH.sub.2 and
--CONH.sub.2;
[0025] and a polymeric dispersant having via a linking group
covalently linked to its polymeric backbone at least one pending
chromophore group which has a molecular weight smaller than 95% of
the molecular weight of said colour pigment.
DISCLOSURE OF THE INVENTION
Definitions
[0026] The term "colorant", as used in disclosing the present
invention, means dyes and pigments.
[0027] The term "dye", as used in disclosing the present invention,
means a colorant having a solubility of 10 mg/L or more in the
medium in which it is applied and under the ambient conditions
pertaining.
[0028] The term "pigment" is defined in DIN 55943, herein
incorporated by reference, as a colouring agent that is practically
insoluble in the application medium under the pertaining ambient
conditions, hence having a solubility of less than 10 mg/L
therein.
[0029] The term "chromophore group", as used in disclosing the
present invention, means a group with an absorption maximum between
300 nm and 2000 nm.
[0030] The term "pending chromophore group", as used in disclosing
the present invention, means a chromophore group occurring as a
side group on the polymeric backbone and not a group in the
polymeric backbone itself or occurring solely as an end group of
the polymeric backbone.
[0031] The term "C.I." is used in disclosing the present
application as an abbreviation for Colour Index.
[0032] The term "actinic radiation" as used in disclosing the
present invention, means electromagnetic radiation capable of
initiating photochemical reactions.
[0033] The term "DP" is used in disclosing the present application
as an abbreviation for degree of polymerization, i.e. the number of
structural units (monomers) in the average polymer molecule.
[0034] The term "PD" is used in disclosing the present application
as an abbreviation for polydispersity of a polymer.
[0035] The term "dispersion", as used in disclosing the present
invention, means an intimate mixture of at least two substances,
one of which, called the dispersed phase or colloid, is uniformly
distributed in a finely divided state through the second substance,
called the dispersion medium.
[0036] The term "polymeric dispersant", as used in disclosing the
present invention, means a substance for promoting the formation
and stabilization of a dispersion of one substance in a dispersion
medium.
[0037] The term "copolymer", as used in disclosing the present
invention means a macromolecule in which two or more different
species of monomer are incorporated into a polymer chain.
[0038] The term "block copolymer", as used in disclosing the
present invention, means a copolymer in which the monomers occur in
relatively long alternate sequences in a chain.
[0039] The term "spectral separation factor" as used in disclosing
the present invention means the value obtained by calculating the
ratio of the maximum absorbance A.sub.max (measured at wavelength
.lamda.max) over the reference absorbance A.sub.ref determined at a
higher wavelength .lamda..sub.ref.
[0040] The abbreviation "SSF" is used in disclosing the present
invention for spectral separation factor.
[0041] The term "alkyl" means all variants possible for each number
of carbon atoms in the alkyl group i.e. for three carbon atoms:
n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl
and tertiary-butyl; for five carbon atoms: n-pentyl,
1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl etc.
[0042] The term "acyl group" means --(C.dbd.O)-aryl and
--(C.dbd.O)-alkyl groups. The term "aliphatic group" means
saturated straight chain, branched chain and alicyclic hydrocarbon
groups.
[0043] The term "unsaturated aliphatic group" means straight chain,
branched chain and alicyclic hydrocarbon groups which contain at
least one double or triple bond.
[0044] The term "aromatic group" as used in disclosing the present
invention means an assemblage of cyclic conjugated carbon atoms,
which are characterized by large resonance energies, e.g. benzene,
naphthalene and anthracene.
[0045] The term "alicyclic hydrocarbon group" means an assemblage
of cyclic carbon atoms, which do not form an aromatic group, e.g.
cyclohexane.
[0046] The term "heteroaromatic group" means an aromatic group
wherein at least one of the cyclic conjugated carbon atoms is
replaced by a non-carbon atom such as a nitrogen atom, a sulphur
atom, a phosphorous atom, selenium atom and a tellurium atom.
[0047] The term "heterocyclic group" means an alicyclic hydrocarbon
group wherein at least one of the cyclic carbon atoms is replaced
by an oxygen atom, a nitrogen atom, a phosphorous atom, a silicon
atom, a sulphur atom, a selenium atom or a tellurium atom.
Pigmented Inkjet Ink
[0048] The pigmented inkjet ink according to the present invention
contains at least three components: (i) a colour pigment, (ii) a
polymeric dispersant, and (iii) a dispersion medium.
[0049] The pigmented inkjet ink according to the present invention
may further contain at least one surfactant.
[0050] The pigmented inkjet ink according to the present invention
may further contain at least one biocide.
[0051] The pigmented inkjet ink according to the present invention
may further contain at least one humectant and/or penetrant.
[0052] The pigmented inkjet ink according to the present invention
may further contain at least one pH adjuster.
[0053] The pigmented inkjet ink according to the present invention
may contain at least one humectant to prevent the clogging of the
nozzle, due to its ability to slow down the evaporation rate of
ink.
[0054] The viscosity of the pigmented inkjet ink according to the
present invention is preferably lower than 100 mPas, more
preferably lower than 30 mPas, and most preferably lower than 15
mPas at a shear rate of 100 s.sup.-1 and a temperature between 20
and 110.degree. C.
[0055] The pigmented inkjet ink according to the present invention
is preferably an aqueous, a solvent based or an oil based pigmented
inkjet ink.
[0056] The pigmented inkjet ink according to the present invention
may be curable and may contain monomers, oligomers and/or
prepolymers possessing different degrees of functionality. A
mixture including combinations of mono-, di-, tr- and/or higher
functionality monomers, oligomers or prepolymers may be used. The
initiator typically initiates the polymerization reaction. A
catalyst called an initiator for initiating the polymerization
reaction may be included in the curable pigmented inkjet ink. The
initiator can be a thermal initiator, but is preferably a
photo-initiator. The photo-initiator requires less energy to
activate than the monomers, oligomers and/or prepolymers to form
the polymer. The photo-initiator suitable for use in the curable
fluid may be a Norrish type I initiator, a Norrish type II
initiator or a photo-acid generator.
Colour Pigments
[0057] The colour pigment used in the pigmented inkjet ink
according to the present invention is represented by formula
(I)
##STR00003##
[0058] wherein,
[0059] R1 to R10 are independently selected from the group
consisting of hydrogen, a halogen atom, a methyl group, an ethyl
group, a methoxy group, an ethoxy group, --CF.sub.3, --COOH,
--COOCH.sub.3; --SO.sub.2NH--C.sub.6H.sub.5,
--CONH--C.sub.6H.sub.5, --CONH--C.sub.6H.sub.5--CONH.sub.2 and
--CONH.sub.2;
[0060] and a polymeric dispersant having via a linking group
covalently linked to its polymeric backbone at least one pending
chromophore group which has a molecular weight smaller than 95% of
the molecular weight of said colour pigment.
[0061] In a preferred embodiment R2, R4, R5, R7, R9 and R10 in
Formula (I) are hydrogen.
[0062] The colour pigment may be chosen from those disclosed by
HERBST, Willy, et al. Industrial Organic Pigments, Production,
Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN
3527305769.
[0063] Particular preferred pigments are C.I. Pigment Yellow 155
and 198.
[0064] The pigment particles in the pigmented inkjet ink should be
sufficiently small to permit free flow of the ink through the
inkjet printing device, especially at the ejecting nozzles. It is
also desirable to use small particles for maximum colour strength
and to slow down sedimentation.
[0065] The average particle size of the pigment in the pigmented
inkjet ink should be between 0.005 and 15 .mu.m. Preferably, the
average pigment particle size is between 0.005 and 5 .mu.m, more
preferably between 0.005 and 1 .mu.m, particularly preferably
between 0.005 and 0.3 .mu.m and most preferably between 0.040 and
0.150 .mu.m. Larger pigment particle sizes may be used as long as
the objectives of the present invention are achieved.
[0066] The pigment is used in the pigmented inkjet ink in an amount
of 0.1 to 20 wt %, preferably 1 to 10 wt % based on the total
weight of the pigmented inkjet ink.
Polymeric Dispersants
[0067] The polymeric dispersant used in the pigmented inkjet ink
according to the present invention contains one or more pending
chromophore groups linked by a linking group to a polymeric
backbone.
[0068] The polymeric dispersant used in the pigmented inkjet ink
according to the present invention preferably has a polymeric
backbone with a polymerization degree DP between 5 and 1000, more
preferably between 10 and 500 and most preferably between 10 and
100.
[0069] The polymeric dispersant used in the pigmented inkjet ink
according to the present invention preferably has a number average
molecular weight Mn between 500 and 30000, more preferably between
1500 and 10000.
[0070] The polymeric dispersant has preferably a polymeric
dispersity PD smaller than 2, more preferably smaller than 1.75 and
most preferably smaller than 1.5.
[0071] The polymeric dispersant is used in the pigmented inkjet ink
in an amount of 5 to 600 wt %, preferably 10 to 100 wt % based on
the weight of the pigment.
Polymeric Backbones
[0072] The polymeric backbone of the polymeric dispersant used in
the pigmented inkjet ink according to the present invention is
required for the compatibility between polymeric dispersant and
dispersion medium.
[0073] It is not required that the polymeric backbone has an
affinity for the pigment. For example, the polymeric backbone of a
dispersant for aqueous inkjet inks can be a homopolymer of acrylic
acid monomers. A homopolymer is generally incapable of dispersing
pigments, but the presence of a pending chromophore group
exhibiting a similarity with the pigment ensures an adequate
affinity between polymeric dispersant and pigment surface.
[0074] The polymeric backbone can also be a statistical copolymer,
a block copolymer, a graft copolymer, a comb polymer or an
alternating copolymer. Also suitable as polymeric backbone is a
gradient copolymer as disclosed by MATYJASZEWSKI, K., et al. Atom
Transfer Radical Polymerization. Chem. Reviews 2001. vol. 101, p.
2921-2990. Sometimes it can be useful to include a number of
monomers with a high affinity for the pigment surface to enhance
certain properties of the inks, e.g. dispersion stability. For
example, the polymeric backbone of a dispersant for aqueous inkjet
inks may contain hydrophobic monomers to increase the affinity of
the polymeric dispersant for the pigment surface. However in
enhancing this affinity for the pigment surface, care should be
taken that enough of the polymeric backbone sticks out to make the
pigment particles compatible with the dispersion medium.
[0075] In graft copolymers the use of grafted chains of
methoxypolyethyleneglycol (MPEG) has been found to be very
advantageous in aqueous inkjet inks. For solvent-based inkjet inks
the use of grafted chains of polyester were found to be very
advantageous. A preferred MPEG macromonomer is BISOMER.TM. MPEG
350MA (methoxypolyethyleneglycol methacrylate) from LAPORTE
INDUSTRIES LTD.
[0076] Preferred grafted chains of polyester in non-aqueous inkjet
inks are derived from .delta.-valerolactone, .epsilon.-caprolactone
and/or C.sub.1 to C.sub.4 alkyl substituted .epsilon.-caprolactone.
The grafted chains can be introduced into the polymeric dispersant
through CDI coupling of a polyester-OH chain with a carboxylic acid
group of, for example, an acrylic acid monomer in the polymeric
backbone of the dispersant. However, it was observed that grafting
by free radical polymerization, wherein the polyester chain already
coupled to the carboxylic acid group of an acrylic acid monomer was
used as a macro-monomer, not only resulted in better dispersion
quality and stability of the inkjet inks but also were obtained by
a more reproducible polymeric dispersant synthesis requiring less
purification.
[0077] For radiation curable inks with the dispersion medium
comprising or consisting of monomers and/or oligomers, many
(co)polymers having good solubility in the dispersion medium were
found to be suitable for the polymer backbone of the polymeric
dispersant;
[0078] The copolymeric backbone consists preferably of no more than
2 or 3 monomer species.
[0079] The monomers and/or oligomers used to prepare the polymeric
dispersant used in the pigmented inkjet ink according to the
present invention can be any monomer and/or oligomer found in the
Polymer Handbook, Vol. 1+2. 4th edition. Edited by J. BRANDRUP, et
al. Wiley-Interscience, 1999.
[0080] Suitable examples of monomers include: acrylic acid,
methacrylic acid, maleic acid, acryloyloxybenzoic acid and
methacryloyloxybenzoic acid (or their salts), maleic anhydride;
alkyl(meth)acrylates (linear, branched and cycloalkyl) such as
methyl(meth)acrylate, n-butyl(meth)acrylate,
tert-butyl(meth)acrylate, cyclohexyl(meth)acrylate and
2-ethylhexyl(meth)acrylate; aryl(meth)acrylates such as
benzyl(meth)acrylate and phenyl(meth)acrylate;
hydroxyalkyl(meth)acrylates such as hydroxyethyl(meth)acrylate and
hydroxypropyl(meth)acrylate; (meth)acrylates with other types of
functionalities (e.g. oxirane, amino, fluoro, polyethylene oxide,
phosphate-substituted) such as glycidyl(meth)acrylate,
dimethylaminoethyl(meth)acrylate, trifluoroethyl acrylate,
methoxypolyethyleneglycol (meth)acrylate and
tripropyleneglycol(meth)acrylate phosphate; allyl derivatives such
as allyl glycidyl ether; styrenics such as styrene,
4-methylstyrene, 4-hydroxystyrene, and 4-acetoxystyrene;
(meth)acrylonitrile; (meth)acrylamides (including N-mono and
N,N-disubstituted) such as N-benzyl (meth)acrylamide; maleimides
such as N-phenyl maleimide, N-benzyl maleimide and N-ethyl
maleimide; vinyl derivatives such as vinylcaprolactam,
vinylpyrrolidone, vinylimidazole, vinylnaphthalene and vinyl
halides; vinylethers such as vinylmethyl ether; and vinylesters of
carboxylic acids such as vinylacetate and vinylbutyrate.
Linking Groups
[0081] The pending chromophore group is linked by a linking group
to the polymeric backbone. The linking group contains at least one
carbon atom, one nitrogen atom, one oxygen atom, one phosphorous
atom, one silicon atom, one sulphur atom, one selenium atom or one
tellurium atom.
[0082] The linking group has preferably a molecular weight smaller
than the molecular weight of the pending chromophore group, more
preferably the linking group has a molecular weight smaller than
80% than the molecular weight of the pending chromophore group, and
most preferably the linking group has a molecular weight smaller
than 50% than the molecular weight of the pending chromophore
group.
[0083] In one embodiment, the linking group is the result of
modification of a (co)polymer with a chromophore having a reactive
group. Suitable reactive groups on the chromophore include thiol
groups, primary or secondary amino groups, carboxylic acid groups
or salts thereof, hydroxyl groups, isocyanate groups and epoxy
groups. Typical covalent bonds formed by reaction of the
chromophore with the polymeric backbone include an amide, an ester,
a urethane, an ether and a thioether.
[0084] In another embodiment, the polymeric dispersant is prepared
by copolymerizing monomers of the polymeric backbone and monomers
containing a chromophore group. In this case the linking group is
already present in the monomer. This polymerization method offers
the advantage of well-controlled design of polymeric dispersants
for a wide variety of dispersion media. Due to its low solubility,
a monomer containing the complete colour pigment as a chromophore
group poses problems both in the synthesis of the polymeric
dispersants, as well as the suitability of the polymeric dispersant
for a wide variety of dispersion media and pigments.
Pending Chromophore Groups
[0085] The pending chromophore group of the polymeric dispersant
used in the pigmented inkjet ink according to the present invention
exhibits a high similarity with the colour pigment of the pigmented
inkjet ink, and has a molecular weight which is smaller than 90%,
preferably smaller than 85%, more preferably smaller than 75% and
most preferably smaller than 65% of the molecular weight of the
colour pigment.
[0086] The pending chromophore group of the polymeric dispersant
may be represented by formula (II):
##STR00004##
[0087] wherein,
[0088] one of L1, L2 or L3 is said linking group and is selected
from the group consisting of an aliphatic group, a substituted
aliphatic group, an unsaturated aliphatic group and a substituted
unsaturated aliphatic group;
[0089] L1, L2 and/or L3, if not representing said linking group,
are independently selected from the group consisting of hydrogen,
an alkyl group, an alkenyl group, an alkoxy group, a carboxylic
acid group, an ester group, an acyl group, a nitro group and a
halogen;
[0090] AR1 and AR2 represent an aromatic group; and
[0091] n represents the integer 0 or 1.
[0092] The linking groups L1 and L3 in the pending chromophore
group according to Formula (II) consist of all atoms between the
polymeric backbone and the first atom of the aromatic group by
which the pending chromophore group is linked to the polymeric
backbone. The linking group L2 in the pending chromophore group
according to Formula (II) consists of all atoms between the
polymeric backbone and the carbon atom directly linked to both L2
and the carbonyl group of the acetoacetanilide group in the pending
chromophore group according to Formula (II).
[0093] In a preferred embodiment the pending chromophore group of
the polymeric dispersant may be represented by formula (III):
##STR00005##
[0094] wherein,
[0095] one of R1 to R11 is said linking group forming a covalent
bond with said polymeric backbone;
[0096] R1 to R11, if not representing said linking group, are
independently selected from the group consisting of hydrogen, an
alkyl group, an alkenyl group, an alkoxy group, an alcohol group, a
carboxylic acid group, an ester group, an acyl group, a nitro group
and a halogen; or
[0097] R7 and R8 may together form a heterocyclic ring. Preferably
the heterocyclic ring formed by R7 and R8 is imidazolone or
2,3-dihydroxypyrazine, so that a benzimidazolone ring and a
2,3-dihydroxyquinoxaline ring respectively are formed in Formula
(III).
[0098] Suitable examples of the pending chromophore group
represented by formula (III) having an unreacted linking group
include
##STR00006## ##STR00007## ##STR00008## ##STR00009##
[0099] The pending chromophore group is preferably present in the
range of 1 to 30 percentage, more preferably in the range 5 to 20
percentage based on the monomeric units of the polymeric backbone.
Polymeric dispersants having a homopolymer or statistical copolymer
as polymeric backbone with more than 45 percent of the monomeric
units of the polymeric backbone having pending chromophore groups
exhibit problems of solubility of the polymeric dispersant in the
dispersion medium and deterioration of the dispersing properties
due to the fact that the dispersant would go flat on the pigment
surface. However, in the case of a well-defined block-copolymer a
good dispersion can be obtained with 50 percent of the monomeric
units of the polymeric backbone having pending chromophore groups.
This well-defined block-copolymer preferably has at least one block
containing no pending chromophore groups.
[0100] In some cases, the dispersion stability of the pigment
according to the present invention can be further improved by
increasing the number of pending chromophore groups in the
polymeric dispersant. In a preferred embodiment, two, three or more
pending chromophore groups are located in close proximity of each
other on the polymeric backbone. Close proximity means preferably
less than 50 monomeric units, more preferably less than 20
monomeric units and most preferably less than 10 monomeric units
between two pending chromophore groups. It is believed that the
dispersion stability improvement by more pending chromophore groups
is due to the dynamic character of the attaching and detaching of
the pending chromophore group to the pigment surface. By increasing
the number of pending chromophore groups, the probability that all
pending chromophore groups will be in a "detached state" at the
same time is expected to decrease.
Synthesis
[0101] The polymerization process may be a condensation
polymerization, in which the chain growth is accompanied by
elimination of small molecules such as water or methanol or an
addition polymerization, in which the polymer is formed without the
loss of other materials. Polymerization of the monomers can be
conducted according to any conventional method such as bulk
polymerization and semi-continuous polymerization.
[0102] The synthesis is preferably performed by a controlled
radical polymerization (CRP) technique. Suitable polymerization
techniques include ATRP (atom transfer radical polymerization),
RAFT (reversible addition-fragmentation chain transfer
polymerization), MADIX (reversible addition-fragmentation chain
transfer process, using a transfer active xanthate), catalytic
chain transfer (e.g. using cobalt complexes), GTP (group transfer
polymerization), or nitroxide (e.g. TEMPO) mediated
polymerizations.
[0103] In one embodiment the polymeric dispersant used in the
pigmented inkjet ink according to the present invention is prepared
by a post-polymerization modification with a chromophore. The
chromophore is covalently linked to the polymer backbone of the
polymeric dispersant. The post-polymerization modification can be
any suitable reaction, e.g. an esterification reaction.
[0104] An esterification reaction suitable for post-polymerization
modification can be performed using N,N'-carbonyldiimidazole (CDI).
In a first step, the carboxylic moieties of the polymer are
activated with CDI to form an intermediate imidazole, which is then
esterified with the chromophore having a reactive hydroxyl group.
The completion of the first step can be observed when the CO.sub.2
degassing stops.
Synthesis Scheme with R Representing the Chromophore Group:
##STR00010##
[0105] Side products of the reaction can be removed by acidifying
the aqueous medium used for precipitation of the polymer
(hydrolysis of remaining activated esters and protonation of
imidazole that remains in water, in this way achieving the
separation from the polymer). If the final modified polymer is
water-soluble (e.g. modified homopolymer of acrylic acid), a
dialysis can be performed to purify the polymer.
[0106] In another embodiment the polymeric dispersant used in the
pigmented inkjet ink according to the present invention is prepared
by a copolymerization with a monomer containing a chromophore
group. It was observed that the pigment-based monomers containing a
chromophore group were stable in the presence of radicals.
Classical free radical polymerization (FRP) techniques for
preparing statistical copolymers in a one reactor polymerization
and ATRP for preparing block copolymers were possible to prepare
the polymeric dispersant used in the present invention.
Monomers with a Chromophore Group
[0107] A monomer with a chromophore group for the preparation of
the polymeric dispersant used in the pigmented inkjet ink according
to the present invention can be represented by the general
formula:
A-L-B
[0108] wherein,
[0109] A represents a polymerisable functional group, preferably an
ethylenically unsatured polymerisable functional group;
[0110] L represents a divalent linking group; and
[0111] B represents a chromophore group.
[0112] In a preferred embodiment, the ethylenically unsatured
polymerisable group is selected from the group consisting of a
styrene, an acrylate, a methacrylate, an acrylamide, a
methacrylamide, a maleimide, a vinyl ester and a vinyl ether.
[0113] The monomer with a chromophore group can be represented by
Formula (GEN-1):
##STR00011##
[0114] wherein,
[0115] AR.sub.1 and AR.sub.2 represent a substituted or
unsubstituted aromatic group and R represents a substituted or
unsubstituted aliphatic group, with the proviso that one of R,
AR.sub.1, and AR.sub.2 has a substituent with a polymerisable
functional group, preferably an ethylenically unsatured
polymerisable functional group.
[0116] In one embodiment AR.sub.2 of Formula (GEN-1) is replaced by
an alkyl group, preferably methyl or ethyl.
[0117] In another embodiment AR.sub.2 of Formula (GEN-1) is
replaced by an aliphatic substituent with a polymerisable
functional group, preferably an ethylenically unsatured
polymerisable functional group. Preferably this aliphatic
ethylenically unsatured polymerisable functional group is
represented by
##STR00012##
[0118] Suitable monomers according to Formula (GEN-1) include the
monomers disclosed in Table 1: styrene derivatives, in Table 2:
(meth)acrylate and (meth)acrylamide derivatives, and in Table 3:
other polymerizable derivatives.
TABLE-US-00001 TABLE 1 ##STR00013## ##STR00014## ##STR00015##
##STR00016## ##STR00017## ##STR00018## ##STR00019##
TABLE-US-00002 TABLE 2 ##STR00020## ##STR00021## ##STR00022##
##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027##
##STR00028## ##STR00029##
TABLE-US-00003 TABLE 3 ##STR00030## ##STR00031## ##STR00032##
Dispersion Media
[0119] The dispersion medium used in the pigmented inkjet ink
according to the present invention is a liquid. The dispersion
medium may consist of water and/or organic solvent(s).
[0120] If the pigmented inkjet ink is a curable pigmented inkjet
ink, water and/or organic solvent(s) are replaced by one or more
monomers and/or oligomers to obtain a liquid dispersion medium.
Sometimes, it can be advantageous to add a small amount of an
organic solvent to improve the dissolution of the dispersant. The
content of organic solvent should be lower than 20 wt % based on
the total weight of the pigmented inkjet ink.
[0121] Suitable organic solvents include alcohols, aromatic
hydrocarbons, ketones, esters, aliphatic hydrocarbons, higher fatty
acids, carbitols, cellosolves, higher fatty acid esters. Suitable
alcohols include, methanol, ethanol, propanol and 1-butanol,
1-pentanol, 2-butanol, t.-butanol. Suitable aromatic hydrocarbons
include toluene, and xylene. Suitable ketones include methyl ethyl
ketone, methyl isobutyl ketone, 2,4-pentanedione and
hexafluoroacetone. Also glycol, glycolethers, N-methylpyrrolidone,
N,N-dimethylacetamid, N,N-dimethylformamid may be used.
[0122] Suitable monomers and oligomers can be found in Polymer
Handbook, Vol. 1+2. 4th edition. Edited by J. BRANDRUP, et al.
Wiley-Interscience, 1999.
[0123] Suitable examples of monomers for curable pigmented inkjet
inks include: acrylic acid, methacrylic acid, maleic acid (or their
salts), maleic anhydride; alkyl(meth)acrylates (linear, branched
and cycloalkyl) such as methyl(meth)acrylate,
n-butyl(meth)acrylate, tert-butyl(meth)acrylate,
cyclohexyl(meth)acrylate and 2-ethylhexyl(meth)acrylate;
aryl(meth)acrylates such as benzyl(meth)acrylate and
phenyl(meth)acrylate; hydroxyalkyl(meth)acrylates such as
hydroxyethyl(meth)acrylate and hydroxypropyl(meth)acrylate;
(meth)acrylates with other types of functionalities (e.g. oxirane,
amino, fluoro, polyethylene oxide, phosphate-substituted) such as
glycidyl (meth)acrylate, dimethylaminoethyl(meth)acrylate,
trifluoroethyl acrylate, methoxypolyethyleneglycol (meth)acrylate
and tripropyleneglycol(meth)acrylate phosphate; allyl derivatives
such as allyl glycidyl ether; styrenics such as styrene,
4-methylstyrene, 4-hydroxystyrene, and 4-acetoxystyrene;
(meth)acrylonitrile; (meth)acrylamides (including N-mono and
N,N-disubstituted) such as N-benzyl(meth)acrylamide; maleimides
such as N-phenyl maleimide, N-benzyl maleimide and N-ethyl
maleimide; vinyl derivatives such as vinylcaprolactam,
vinylpyrrolidone, vinylimidazole, vinyinaphthalene and vinyl
halides; vinylethers such as vinylmethyl ether; and vinylesters of
carboxylic acids such as vinylacetate and vinylbutyrate.
[0124] A combination of monomers, oligomers and/or prepolymers may
also be used. The monomers, oligomers and/or prepolymers may
possess different degrees of functionality, and a mixture including
combinations of mono-, di-, tri- and higher functionality monomers,
oligomers and/or prepolymers may be used.
[0125] For oil based inkjet inks the dispersion medium can be any
suitable oil including aromatic oils, paraffinic oils, extracted
paraffinic oils, naphthenic oils, extracted napthenic oils,
hydrotreated light or heavy oils, vegetable oils and derivatives
and mixtures thereof. Paraffinic oils can be normal paraffin types
(octane and higher alkanes), isoparaffins (isooctane and higher
iso-alkanes) and cycloparaffins (cyclooctane and higher
cyclo-alkanes) and mixtures of paraffin oils.
Surfactants
[0126] The pigmented inkjet ink according to the present invention
may contain at least one surfactant. The surfactant(s) can be
anionic, cationic, non-ionic, or zwitter-ionic and are usually
added in a total quantity less than 20 wt % based on the total
weight of the pigmented inkjet ink and particularly in a total less
than 10 wt % based on the total weight of the pigmented inkjet
ink.
[0127] Suitable surfactants for the pigmented inkjet ink according
to the present invention include fatty acid salts, ester salts of a
higher alcohol, alkylbenzene sulphonate salts, sulphosuccinate
ester salts and phosphate ester salts of a higher alcohol (for
example, sodium dodecylbenzenesulphonate and sodium
dioctylsulphosuccinate), ethylene oxide adducts of a higher
alcohol, ethylene oxide adducts of an alkylphenol, ethylene oxide
adducts of a polyhydric alcohol fatty acid ester, and acetylene
glycol and ethylene oxide adducts thereof (for example,
polyoxyethylene nonylphenyl ether, and SURFYNOL.TM. 104, 104H, 440,
465 and TG available from AIR PRODUCTS & CHEMICALS INC.).
Biocides
[0128] Suitable biocides for the pigmented inkjet ink of the
present invention include sodium dehydroacetate, 2-phenoxyethanol,
sodium benzoate, sodium pyridinethion-1-oxide, ethyl
p-hydroxybenzoate and 1,2-benzisothiazolin-3-one and salts
thereof.
[0129] Preferred biocides are Bronidox.TM. available from HENKEL
and Proxel.TM. GXL available from AVECIA.
[0130] A biocide is preferably added in an amount of 0.001 to 3 wt
%, more preferably 0.01 to 1.00 wt %, each based on the total
weight of the pigmented inkjet ink.
pH Adjusters
[0131] The pigmented inkjet ink according to the present invention
may contain at least one pH adjuster. Suitable pH adjusters include
NaOH, KOH, NEt.sub.3, NH.sub.3, HCl, HNO.sub.3, H.sub.2SO.sub.4 and
(poly)alkanolamines such as triethanolamine and
2-amino-2-methyl-1-propanol. Preferred pH adjusters are NaOH and
H.sub.2SO.sub.4.
Humectants/Penetrants
[0132] Suitable humectants include triacetin,
N-methyl-2-pyrrolidone, glycerol, urea, thiourea, ethylene urea,
alkyl urea, alkyl thiourea, dialkyl urea and dialkyl thiourea,
diols, including ethanediols, propanediols, propanetriols,
butanediols, pentanediols, and hexanediols; glycols, including
propylene glycol, polypropylene glycol, ethylene glycol,
polyethylene glycol, diethylene glycol, tetraethylene glycol, and
mixtures and derivatives thereof. Preferred humectants are
triethylene glycol mono butylether, glycerol and 1,2-hexanediol.
The humectant is preferably added to the inkjet ink formulation in
an amount of 0.1 to 40 wt % of the formulation, more preferably 0.1
to 10 wt % of the formulation, and most preferably approximately
4.0 to 6.0 wt %.
Preparation of a Pigmented Inkjet Ink
[0133] The pigmented inkjet ink according to the present invention
may be prepared by precipitating or milling the pigment in the
dispersion medium in the presence of the polymeric dispersant.
[0134] Mixing apparatuses may include a pressure kneader, an open
kneader, a planetary mixer, a dissolver, and a Dalton Universal
Mixer. Suitable milling and dispersion apparatuses are a ball mill,
a pearl mill, a colloid mill, a high-speed disperser, double
rollers, a bead mill, a paint conditioner, and triple rollers. The
dispersions may also be prepared using ultrasonic energy.
[0135] Many different types of materials may be used as milling
media, such as glasses, ceramics, metals, and plastics. In a
preferred embodiment, the grinding media can comprise particles,
preferably substantially spherical in shape, e.g. beads consisting
essentially of a polymeric resin or yttrium stabilized zirconium
beads.
[0136] In the process of mixing, milling and dispersion, each
process is preferably performed with cooling to prevent build up of
heat.
[0137] In the process of mixing, milling and dispersion, each
process is performed with cooling to prevent build up of heat, and
for radiation curable inkjet inks as much as possible under light
conditions in which actinic radiation has been substantially
excluded.
[0138] The inkjet ink according to the present invention may
contain more than one pigment, the inkjet ink may be prepared using
separate dispersions for each pigment, or alternatively several
pigments may be mixed and co-milled in preparing the
dispersion.
[0139] The dispersion process can be carried out in a continuous,
batch or semi-batch mode.
[0140] The preferred amounts and ratios of the ingredients of the
mill grind will vary widely depending upon the specific materials
and the intended applications. The contents of the milling mixture
comprise the mill grind and the milling media. The mill grind
comprises pigment, polymeric dispersant and a liquid carrier such
as water. For inkjet inks, the pigment is usually present in the
mill grind at 1 to 50 wt %, excluding the milling media. The weight
ratio of pigment over polymeric dispersant is 20:1 to 1:2.
[0141] The milling time can vary widely and depends upon the
pigment, mechanical means and residence conditions selected, the
initial and desired final particle size, etc. In the present
invention pigment dispersions with an average particle size of less
than 100 nm may be prepared.
[0142] After milling is completed, the milling media is separated
from the milled particulate product (in either a dry or liquid
dispersion form) using conventional separation techniques, such as
by filtration, sieving through a mesh screen, and the like. Often
the sieve is built into the mill, e.g. for a bead mill. The milled
pigment concentrate is preferably separated from the milling media
by filtration.
[0143] In general it is desirable to make the inkjet inks in the
form of a concentrated mill grind, which is subsequently diluted to
the appropriate concentration for use in the inkjet printing
system. This technique permits preparation of a greater quantity of
pigmented ink from the equipment. By dilution, the inkjet ink is
adjusted to the desired viscosity, surface tension, colour, hue,
saturation density, and print area coverage for the particular
application.
Spectral Separation Factor
[0144] The spectral separation factor SSF was found to be an
excellent measure to characterize a pigmented inkjet ink, as it
takes into account properties related to light-absorption (e.g.
wavelength of maximum absorbance .lamda..sub.max, shape of the
absorption spectrum and absorbance-value at .lamda..sub.max) as
well as properties related to the dispersion quality and
stability.
[0145] A measurement of the absorbance at a higher wavelength gives
an indication on the shape of the absorption spectrum. The
dispersion quality can be evaluated based on the phenomenon of
light scattering induced by solid particles in solutions. When
measured in transmission, light scattering in pigment inks may be
detected as an increased absorbance at higher wavelengths than the
absorbance peak of the actual pigment. The dispersion stability can
be evaluated by comparing the SSF before and after a heat treatment
of e.g. a week at 80.degree. C.
[0146] The spectral separation factor SSF of the ink is calculated
by using the data of the recorded spectrum of an ink solution or a
jetted image on a substrate and comparing the maximum absorbance to
the absorbance at a higher reference wavelength .lamda..sub.ref.
The spectral separation factor is calculated as the ratio of the
maximum absorbance A.sub.max over the absorbance A.sub.ref at a
reference wavelength.
SSF = A max A ref ##EQU00001##
[0147] The SSF is an excellent tool to design inkjet ink sets with
large colour gamut. Often inkjet ink sets are now commercialized,
wherein the different inks are not sufficiently matched with each
other. For example, the combined absorption of all inks does not
give a complete absorption over the whole visible spectrum, e.g.
"gaps" exist between the absorption spectra of the colorants.
Another problem is that one ink might be absorbing in the range of
another ink. The resulting colour gamut of these inkjet ink sets is
low or mediocre.
EXAMPLES
Materials
[0148] All materials used in the following examples were readily
available from standard sources such as Aldrich Chemical Co.
(Belgium) and Acros (Belgium) unless otherwise specified.
[0149] The water used was deionized water.
[0150] SMA 1000P is a styrene maleic anhydride alternating
copolymer available from ATOFINA.
[0151] Raney Nickel.TM. is a catalysator from DEGUSSA.
[0152] WAKO V-601 is dimethyl 2,2'-azobisisobutyrate from Wako Pure
Chemical Industries, Ltd.
[0153] MSTY or alpha methylstyrene dimer is
2,4-diphenyl-4-methyl-1-pentene from Goi Chemical Co., Ltd.
[0154] AA is acrylic acid from ACROS.
[0155] MAA is methacrylic acid from ACROS.
[0156] BA is butyl acrylate from ACROS.
[0157] EHA is 2-ethyl hexyl acrylate from ACROS.
[0158] STY is styrene from ACROS.
[0159] Proxel.TM. Ultra 5 from AVECIA.
[0160] Glycerol from ACROS.
[0161] 1,2-propanediol from CALDIC CHEMIE NV.
[0162] Surfynol.TM. 104H from AIR PRODUCTS & CHEMICALS INC.
[0163] PY155 is the abbreviation for C.I. Pigment Yellow 155 for
which Ink jet Yellow 4G VP 2532 from Clariant was used.
##STR00033##
Measurement Methods
1. Measurement of SSF
[0164] The spectral separation factor SSF of the ink was calculated
by using the data of the recorded spectrum of an ink solution and
comparing the maximum absorbance to the absorbance at a reference
wavelength. The choice of this reference wavelength is dependent on
the pigment(s) used: [0165] if the colour ink has a maximum
absorbance A.sub.max between 400 and 500 nm then the absorbance
A.sub.ref must be determined at a reference wavelength of 600 nm,
[0166] If the colour ink has a maximum absorbance A.sub.max between
500 and 600 nm then the absorbance A.sub.ref must be determined at
a reference wavelength of 650 nm, [0167] If the colour ink has a
maximum absorbance A.sub.max between 600 and 700 nm then the
absorbance A.sub.ref must be determined at a reference wavelength
of 830 nm.
[0168] The absorbance was determined in transmission with a
Shimadzu UV-2101 PC double beam-spectrophotometer. The ink was
diluted to have a pigment concentration of 0.002%. In the case of a
magenta ink, the ink was diluted to have a pigment concentration of
0.005%. A spectrophotometric measurement of the UV-VIS-NIR
absorption spectrum of the diluted ink was performed in
transmission-mode with a double beam-spectrophotometer using the
settings of Table 4. Quartz cells with a path length of 10 mm were
used and water was chosen as a blank.
TABLE-US-00004 TABLE 4 Mode Absorbance Wavelength range 240-900 nm
Slit width 2.0 nm Scan interval 1.0 nm Scan speed Fast (1165
nm/min) Detector photo-multiplier(UV-VIS)
[0169] Efficient pigmented inkjet inks exhibiting a narrow
absorption spectrum and a high maximum absorbance have a value for
SSF of at least 30.
2. Dispersion Stability
[0170] The dispersion stability was evaluated by comparing the SSF
before and after a heat treatment of one week at 80.degree. C.
Pigmented inkjet inks exhibiting good dispersion stability have a
SSF after heat treatment still larger than 30.
3. Polymer Analysis
[0171] Unless otherwise specified all polymers have been
characterized with gel permeation chromatography (GPC) and nuclear
magnetic resonance spectroscopy (NMR) using the following methods.
Random or block copolymers were analyzed with NMR by dissolving
them in a deuterated solvent. For .sup.1H-NMR.+-.20 mg polymer was
dissolved in 0.8 mL CDCl.sub.3 or DMSO-d6 or acetonitrile-d3 or
D.sub.2O (with or without NaOD addition).
[0172] Spectra were recorded on a Varian Inova 400 MHz instrument
equipped with an ID-probe. For .sup.13C-NMR.+-.200 mg polymer was
dissolved in 0.8 mL CDCl.sub.3 or DMSO-d6 or acetonitrile-d3 or
D.sub.2O (with or without NaOD addition). Spectra were recorded on
a Varian Gemini2000 300 MHz equipped with a SW-probe.
[0173] Mn, Mw and polydispersity (PD) values were determined using
gel permeation chromatography. For polymers dissolvable in organic
solvents PL-mixed B columns (Polymer Laboratories Ltd) were used
with THF+5% acetic acid as mobile phase using polystyrene with
known molecular weights as calibration standards. These polymers
were dissolved in the mobile phase at a concentration of 1 mg/mL.
For polymers dissolvable in water PL Aquagel OH-60, OH-50, OH-40
and/or OH-30 (Polymer Laboratories Ltd) column combinations were
used depending on the molecular weight region of the polymers under
investigation. As mobile phase water/methanol mixtures adjusted to
pH 9.2 with e.g. disodiumhydrogen phosphate were used with or
without the addition of neutral salts e.g. sodium nitrate. As
calibration standards polyacrylic acids with known molecular
weights were used. The polymers were dissolved in either water or
water made basic with ammonium hydroxide at a concentration of 1
mg/mL. Refractive index detection was used.
[0174] An example is now given to illustrate the calculation of the
average composition of a random (=statistical) copolymer
P(MAA-c-EHA).
[0175] The Mn of the copolymer was determined with GPC to be
5000.
[0176] The molar percentage of each monomer type by NMR was
determined to be: 45 mole % MAA and 55 mole % EHA.
[0177] Calculation:
(0.45.times.M.sub.MAA)+(0.55.times.M.sub.EHA)=140.09
5000/140.09=total number of monomeric units in average polymer
chain=36
Average number of MAA units=0.45.times.(5000/140.09)=16 units
Average number of EHA units=0.55.times.(5000/140.09)=20 units
[0178] Thus, the average composition is
P(MAA.sub.16-c-EHA.sub.20).
4: Particle Size
[0179] The particle size of pigment particles in pigmented inkjet
ink was determined by photon correlation spectroscopy at a
wavelength of 633 nm with a 4 mW HeNe laser on a diluted sample of
the pigmented inkjet ink.
[0180] The particle size analyzer used was a Malvern.TM. nano-S
available from Goffin-Meyvis.
[0181] The sample was prepared by addition of one drop of ink to a
cuvet containing 1.5 mL water and mixed until a homogenous sample
was obtained. The measured particle size is the average value of 3
consecutive measurements consisting of 6 runs of 20 seconds. For
good ink jet characteristics (jetting characteristics and print
quality) the average particle size, of the dispersed particles is
preferably below 150 nm.
5. Calculation of % MW
[0182] The % MW is calculated as the ratio of the molecular weight
of the pending chromophore group over the molecular weight of the
colour pigment multiplied by 100.
Example 1
[0183] This example illustrates that pigments in accordance with
the present invention can be dispersed in inkjet inks using a
polymeric dispersant having one or more pending chromophore groups
that are smaller but similar in chemical structure to the pigment.
The polymeric backbone of the dispersant was an alternating
polymer, which is known to have poor dispersing capability.
Polymeric Dispersants DISP-1 to DISP-3
[0184] The alternating copolymer SMA 1000P was used as polymeric
dispersant DISP-1 to prepare a comparative inkjet ink.
[0185] DISP-1 was then used for preparing styrene maleic acid
copolymers modified by the chromophores MC--O and MC--P.
TABLE-US-00005 TABLE 5 MC-O ##STR00034## MC-P ##STR00035##
[0186] The synthesis is based on a kinetic study on the
mono-esterification of styrene maleic anhydride copolymers
disclosed by HU, et al. Monoesterification of styrene-maleic
anhydride copolymers with alcohols in ethylbenzene: catalysis and
kinetics. J. Polym. Sci., A, Polym. Chem. 1993, vol. 31, p 691-670.
1993, vol. 31, p. 691-700. The general synthesis scheme is
represented by:
##STR00036##
Chromophore MC--O
[0187] The synthesis of the chromophore MC--O will now be
described.
Preparation of Compound MC-1C
[0188] The vessel used to carry out this reaction was a 3 necked
flask equipped with a stirrer, a cooler and a dropping-funnel. To a
solution of 13.9 g (0.1 mol) 2-nitrophenol (compound MC-1A) in 100
mL dimethylformamide was added 31.8 g (0.3 mol) of sodiumcarbonate.
The mixture was heated to a temperature of about 150-160.degree. C.
and 16.1 g (0.2 mol) of 2-chloroethanol (compound MC-1B) was added
drop-wise. After addition of the 2-chloroethanol, the temperature
was maintained at a temperature between 150 and 160.degree. C. for
about 7 hours. The charge was cooled while stirring and the formed
inorganic salts were filtered off. The filtrate was concentrated by
evaporation at a temperature of 40.degree. C. until a red coloured
mixture of oil and solid was formed. Then the oil was dissolved in
methylenechloride and the inorganic salts were filtered off. The
filtrate was evaporated for a second time and the formed yellow oil
was purified by preparative column chromatography. The yield of
compound MC-1C was 79%.
Synthesis Scheme of Compound MC-1C:
##STR00037##
[0189] Preparation of Compound MC-1D
[0190] Compound MC-1D was made by catalytic reduction of compound
MC-1C with hydrogen.
[0191] A reactor was filled with 18.3 g (0.1 mol) of compound MC-1C
in 100 mL ethanol and 1 mL of Raney Nickel.TM. slurry was added.
The volume of the mixture was set to 150 mL with ethanol and the
reduction was carried out at a starting temperature of 35.degree.
C. under an initial H.sub.2-pressure of 60 bar. By shaking the
reactor, the exothermic reaction started and the temperature
increased to about 60.degree. C. After reduction, the Raney
Nickel.TM. was filtered off. The filtrate was evaporated at a
temperature of 50.degree. C. until the desired white crystalline
product MC-1D appeared. The yield of compound MC-1D was 95%.
Synthesis Scheme of Compound MC-1D:
##STR00038##
[0192] Preparation of Chromophore MC--O
[0193] 6.9 g (45.2 mmol) of compound MC-1D was mixed with 40 mL
H.sub.2O and 10 mL methanol. Then, 4.5 g (54 mmol) of compound
MC-1F was added and the mixture was stirred for 30 minutes. This is
mixture A-MC--O.
[0194] 9.4 g (45.2 mmol) of compound MC--OA was mixed in 50 mL
H.sub.20+50 mL methanol. 16.2 g (162 mmol) of concentrated HCl was
added and the mixture was then cooled to a temperature of about 0
to 5.degree. C. 4.05 g (58.8 mmol) of sodium nitrite was added and
the mixture was kept at a temperature between 0 and 5.degree. C.
After 15 minutes the excess of nitrite was neutralized by adding
1.36 g (13.6 mmol) of sulfamic acid and a pH of 7 was obtained by
adding 11.4 g (136 mmol) of sodium carbonate. The mixture A-MC--O
was added and the mixture was stirred for 1 hour at a temperature
between 0 and 5.degree. C. The yellow product was filtered and
washed with methanol. The yield of the chromophore MC--O was
44%.
Synthesis Scheme of Chromophore MC--O:
##STR00039##
[0195] Chromophore MC--P
[0196] The synthesis of the chromophore MC--P will now be
described.
Preparation of Compound MC-8B
[0197] The vessel used to carry out this reaction was a 3 necked
flask equipped with a stirrer, a cooler and a dropping-funnel. To a
solution of 140 g (1 mol) 3-nitrophenol (compound MC-8A) and 1.4 L
N-methylpyrolidone was added 190 mL sodium methylate 30% (1.025
mol). The mixture was destillated at a temperature of 100.degree.
C. and 80 mbar pressure. After the destillation 87 mL (1.3 mol) of
2-chloroethanol (compound MC-1B) was added dropwise. After addition
of the 2-chloroethanol, the mixture was heated to a temperature of
about 120.degree. C. for 3 hours. The reaction mixture was poured
into 6 L of water with 85 mL HCl conc. The product was filtrated.
The yield of compound MC-8B was 27%.
Synthesis Scheme of Compound MC-8B:
##STR00040##
[0198] Preparation of Compound MC-8C
[0199] Compound MC-8C was made by catalytic reduction of compound
MC-8B with hydrogen.
[0200] A reactor was filled with 101 g (0.55 mol) of compound MC-8B
in 700 mL ethanol and 11 mL of Raney Nickel.TM. slurry was added.
The reduction was carried out at a starting temperature of
75.degree. C. under an initial H.sub.2-pressure of 46 bar. After
reduction, the charge was mixed during 1 hour and the Raney
Nickel.TM. was filtered off. The filtrate was evaporated at a
temperature of 50.degree. C. until the desired white crystalline
product MC-8C appeared. The yield of compound MC-8C was 95%.
Synthesis Scheme of Compound MC-8C:
##STR00041##
[0201] Preparation of Compound MC--P
[0202] 6.9 g (45.2 mmol) of compound MC-8C was mixed with 40 mL
H.sub.2O and 10 mL methanol. Then, 4.5 g (54 mmol) of compound
MC-1F was added and the mixture was stirred for 30 minutes. This is
mixture A-MC--P.
[0203] 6.2 g (45.2 mmol) of compound MC--PA was added to a mixture
of 100 mL H.sub.20 and 50 mL methanol. 16.2 g (162 mmol) of
concentrated HCl was added. The solution was cooled to a
temperature of about 0 to 5.degree. C. 4.05 g (58.8 mmol) of sodium
nitrite was added and the mixture was kept at a temperature between
0 and 5.degree. C. After 15 minutes the excess of nitrite was
neutralized by adding 1.36 g (13.6 mmol) of sulfamic acid and a pH
of 7 was obtained by adding 11.4 g (136 mmol) of sodium carbonate.
The mixture A-MC--P was added and the mixture was stirred for 1
hour at a temperature between 0 and 5.degree. C. The stirring was
continued for 3 hours at a temperature of 20.degree. C. The yellow
product was filtered and washed with methanol. The yield of the
chromophore MC--P was 63%.
##STR00042##
Synthesis of Polymeric Dispersant DISP-2
[0204] Polymeric dispersant DISP-2 was prepared by modifying the
polymeric dispersant DISP-1 with the chromophore MC--O. The
resulting pending chromophore group PC--O was linked by C* to the
polymeric backbone through a linking group L containing an ester
bond,
##STR00043##
Preparation of DISP-2
[0205] The styrene maleic anhydride copolymer SMA 1000P was
dissolved in DMA (dimethylacetamide) as solvent. Then 5 mole % of
MC-0, based on the anhydride units in the polymer, was added and
the reaction was allowed to continue for 24 hours at room
temperature. After 24 hours, the polymer was precipitated with
methyl t-butyl ether, isolated by filtration and washed several
times with methyl t-butyl ether. The isolated polymer was suspended
in water and the pH was adjusted to 10, using 5 N NaOH. The mixture
was stirred until the polymer dissolved. Upon complete dissolution,
the pH was adjusted to 2, using 6N HCl. The polymeric dispersant
was precipitated from the medium, isolated by filtration and dried.
The degree of substitution was determined by
.sup.1H-NMR-spectroscopy and expressed as the percentage of
esterified maleic acid units. The degree of substitution of DISP-2
with the chromophore MC--O was 1%.
Synthesis of Polymeric Dispersant DISP-3
[0206] Polymeric dispersant DISP-3 was prepared by modifying the
polymeric dispersant DISP-1 with the chromophore MC--P. The
resulting pending chromophore group PC--P was linked by C* to the
polymeric backbone through a linking group L containing an ester
bond.
##STR00044##
Preparation of DISP-3
[0207] The styrene maleic anhydride copolymer SMA 1000P was
dissolved in DMA (dimethylacetamide) as solvent. Then 5 mole % of
MC--P, based on the anhydride units in the polymer, was added and
the reaction was allowed to continue for 24 hours at room
temperature. After 24 hours, the polymer was precipitated with
methyl t-butyl ether, isolated by filtration and washed several
times with methyl t-butyl ether. The isolated polymer was suspended
in water and the pH was adjusted to 10, using 5 N NaOH. The mixture
was stirred until the polymer dissolved. Upon complete dissolution,
the pH was adjusted to 2, using 6N HCl. The polymeric dispersant
was precipitated from the medium, isolated by filtration and dried.
The degree of substitution was determined by
.sup.1H-NMR-spectroscopy and expressed as the percentage of
esterified maleic acid units. The degree of substitution of DISP-3
with the chromophore MC--P was 1%.
Preparation of Inkjet Ink
[0208] All inkjet inks were prepared in the same manner to obtain a
composition as described in Table 6, except that different pigments
and dispersants were used.
TABLE-US-00006 TABLE 6 Component wt % Pigment 4.00 Dispersant 2.40
1,2-propanediol 21.00 Glycerol 7.00 Proxel .TM. Ultra 5 0.80
Surfynol .TM. 104H 0.09 Water 64.71
[0209] An ink composition was made by mixing the pigment, the
dispersant and about half of the water with a dissolver and
subsequently treating this mixture with a roller mill procedure
using yttrium-stabilised zirconium oxide-beads of 0.4 mm diameter
("high wear resistant zirconia grinding media" from TOSOH Co.). A
polyethylene flask of 60 mL was filled to half its volume with
grinding beads and 20 g of the mixture. The flask was closed with a
lit and put on the roller mill for three days. The speed was set at
150 rpm. After milling the dispersion was separated from the beads
using a filter cloth. Under stirring, the surfactant Surfynol.TM.
104H and the biocide Proxel.TM. Ultra 5, glycerol, 1,2-propanediol
and the remaining water were added. This mixture was stirred for 10
minutes and filtered. The filtration was performed in two steps.
First, the ink mixture is filtered using a (plastipak) syringe with
a microfiber disposable filtercapsule with 1 .mu.m pore diameter
(GF/B microfiber from Whatman Inc.) Then the same procedure is
repeated on the filtrate. After the second filtration the ink is
ready for evaluation.
[0210] Using the above method, the comparative inkjet ink COMP-1
and the inventive inkjet inks INV-1 and INV-e were prepared
according to Table 7.
TABLE-US-00007 TABLE 7 Polymeric Polymeric Chromophore Colour
InkJet Ink Dispersant backbone Group Pigment COMP-1 DISP-1
Alternating None PY155 INV-1 DISP-2 Alternating PC-O PY155 INV-2
DISP-3 Alternating PC-P PY155
Results and Evaluation
[0211] The spectral separation factor (SSF) was determined for each
sample directly after preparation and was determined again after a
severe heat treatment of 1 week at 80.degree. C. The results are
listed in Table 8.
TABLE-US-00008 TABLE 8 SSF Chromophore Colour 1 week InkJet Ink
Group Pigment % MW SSF 80.degree. C. COMP-1 None PY155 0 6
flocculated INV-1 PC-O PY155 55% 103 32 INV-2 PC-P PY155 55% 61
37
[0212] From Table 8 it is clear that although an alternating
polymer was used as the polymeric backbone of the polymeric
dispersant, the pigments were dispersed exhibiting a high
dispersion quality and a good dispersion stability for the
inventive pigmented inkjet inks INV-1 and INV-2.
Example 2
[0213] This example illustrates the method for preparing the
polymeric dispersants through uncomplicated synthesis with monomers
already containing a chromophore. Since pigments exhibit low
solubility in many solvents, this complicates the synthesis of
polymeric dispersants, which is not witnessed if a chromophore is
used with smaller molecular weight but still exhibiting a
resemblance with the pigment.
Chromophore MC-2
[0214] The formation of the chromophore MC-2 was accomplished by
diazotation of compound MC-1D and subsequent coupling in the
compound MC-2B.
Preparation of Chromophore MC-2
[0215] 29.98 mL (0.36 mol) of concentrated hydrochloric acid was
added to a suspension of 15.3 g (0.1 mol) of compound MC-1D in 300
mL water. This mixture was cooled to a temperature of about
0-5.degree. C. and 8.97 g (0.13 mol) of sodiumnitrite was added.
The diazonium-salt was kept at a temperature between 0 and
5.degree. C. After 15 minutes the excess of nitrite was neutralized
by adding 3.0 g (0.03 mol) of sulfamic acid and a pH of 7 was
obtained by adding 25.2 g (0.3 mol) of sodiumcarbonate. While the
diazionium-salt was made, 20.7 g (0.1 mol) of MC-2B from ACROS was
dissolved in a mixture of 500 mL methanol and 10.0 mL (0.1 mol) 29%
sodiumhydroxide-solution. This solution was added drop-wise into
the diazonium-salt solution and a yellow suspension was immediately
formed. The temperature was maintained between 0 and 5.degree. C.
for about 3 hours and the yellow product MC-2 was filtered and
washed with methanol. The yield of the chromophore MC-2 was
92%.
Synthesis Scheme of the Chromophore MC-2:
##STR00045##
[0216] Polymeric Dispersants DISP-4 to DISP-6
[0217] The polymeric dispersants DISP-4 to DISP-6 were prepared by
copolymerizing a monomer MONC already containing the chromophore
group PC-2.
Synthesis of the Monomer MONC
##STR00046##
[0219] Ethylacetate (480 ml) was cooled to 0.degree. C. Acrylic
acid (19.0 g, 0.264 mol) and 2,6-di-tert-butyl-4-methylphenol (0.2
g, 0.00088 mol) were added. Triethylamine (26.7 g, 0.264 mol) was
added drop-wise while the temperature was maintained between
-5.degree. C. and 0.degree. C. Finally benzene sulfonyl chloride
(22.3 g, 0.126 mol) was added drop-wise. Triethylamine
hydrochloride precipitated. The reaction mixture was allowed to
stir for 1 hour at 0.degree. C. resulting in the formation of the
symmetric anhydride. To this mixture N-hydroxysuccinimide (0.7 g,
0.006 mol) and MC-2 (22.3 g, 0.06 mol) were added at 5.degree. C.
The reaction mixture was refluxed (78.degree. C.) for about 17
hours. The reaction mixture was diluted with EtOAc (100 ml) and
extracted with distilled water (400 ml). The organic layer was
separated and again extracted with a mixture of an aqueous solution
of hydrochloric acid and distilled water (1/5). Finally the organic
layer was washed with water and dried over MgSO.sub.4. After
evaporation of the solvent, the residue was suspended into
distilled water and stirred for 45 minutes. Filtration provided a
yellow solid.
Synthesis Scheme of MONC:
##STR00047##
[0220] Synthesis of Polymeric Dispersant DISP-4
[0221] The polymeric dispersant DISP-4 was prepared by
copolymerizing the monomer MONC with MAA and EHA monomers.
[0222] The synthesis was performed in a 50 ml three-necked round
bottomed flask which was equipped with a cooling unit, a bubble
counter on top and a stirring bar. 1.42 g of the monomer MAA, 3.03
g of the monomer EHA, 1.55 g of the monomer MONC, 0.20 g of the
initiator WAKO.TM. V601, 0.21 g of the transfer agent MSTY were
introduced in 23.59 g of MEK. The total weight % concentration of
the monomers was 20. The reaction mixture was degassed by bubbling
nitrogen in the solution for approximately 30 min. The flask was
immersed into an oil bath and heated to 80.degree. C. and the
mixture was further reacted for 20 hours. After polymerization, the
reaction mixture was cooled down to room temperature. The polymer
was precipitated in 250 ml of water followed by drying under vacuum
at 40.degree. C. for 24 hours to afford 4.5 g of yellow powder of
DISP-4. (Yield=70.2%) Analytical results of DISP-4: GPC: Mn=3893;
Mw=7828; PD=2.01 (aqueous GPC; calibrated vs. PSSA-standards)
[0223] NMR: MAA/EHA/MONC molar ratio was 461-46/8. On average
DISP-4 contained 11 mM monomeric units, 11 EHA monomeric units and
2 MONC monomeric units.
Synthesis of Polymeric Dispersant DISP-5
[0224] The polymeric dispersant DISP-5 was prepared by
copolymerizing the monomer MONC with M and BA monomers.
[0225] The synthesis was performed in a 50 ml three-necked round
bottomed flask which was equipped with a cooling unit, a bubble
counter on top and a stirring bar. 1.47 g of the monomer AA, 2.61 g
of the monomer BA, 1.93 g of the monomer MONC, 0.20 g of the
initiator WAKO.TM. V601, 0.21 g of the transfer agent MSTY were
introduced in 23.59 g of MEK. The total weight % concentration of
the monomers was 20. The reaction mixture was degassed by bubbling
nitrogen in the solution for approximately 30 min. The flask was
immersed into an oil bath and was heated to 80.degree. C. and the
mixture was further reacted for 20 hours. After polymerization, the
reaction mixture was cooled down to room temperature. The polymer
was precipitated in 250 ml of water followed by drying under vacuum
at 40.degree. C. for 24 hours to afford 3.32 g of yellow powder of
DISP-5. (Yield=51.8%) Analytical results of DISP-5: GPC: Mn=5875;
Mw=10853; PD=1.85 (aqueous GPC; calibrated vs. PSSA-standards)
[0226] NMR: AA/BA/MONC molar ratio was 47/43/10. On average DISP-5
contains 21 AA monomeric units, 19 BA monomeric units and 4 MONC
monomeric units.
Synthesis of Polymeric Dispersant DISP-6
[0227] The polymeric dispersant DISP-6 was prepared by
copolymerizing the monomer MONC with M and EHA monomers.
[0228] The synthesis was performed in a 50 ml three-necked round
bottomed flask which was equipped with a cooling unit, a bubble
counter on top and a stirring bar. 1.23 g of the monomer AA, 3.15 g
of the monomer EHA, 1.62 g of the monomer MONC, 0.20 g of the
initiator WAKO.TM. V601, 0.21 g of the transfer agent MSTY were
introduced in 23.59 g of MEK. The total weight % concentration of
the monomers was 20. The reaction mixture was degassed by bubbling
nitrogen in the solution for approximately 30 min. The flask was
immersed into an oil bath and was heated to 80.degree. C. and the
mixture was further reacted for 20 hours. After polymerization, the
reaction mixture was cooled down to room temperature. The polymer
was precipitated in 250 ml of water followed by drying under vacuum
at 40.degree. C. for 24 hours to afford 3.72 g of yellow powder of
DISP-6. (Yield=58.03%) Analytical results of DISP-6: GPC: Mn=4922;
Mw=8320; PD=1.69 (aqueous GPC; calibrated vs. PSSA-standards)
[0229] NMR: AA/EHA/MONC molar ratio was 47/43/10. On average DISP-6
contained 15 AA monomeric units, 14 EHA monomeric units and 3 MONC
monomeric units.
* * * * *